[The inventions described herein may be manufactured, used and licensed by or for the U.S. Government for U.S. Government purposes.]
The invention relates to measuring the velocity of a round exiting a gun barrel. The need for measuring the velocity of a round exiting a gun barrel has existed for a number of years. Since the 1980""s, with the early development of smart bursting ammunition, a need developed for a way to effectively gauge travel time and detonation point of a round. This problem became more acute with the advanced development of anti-personnel air bursting munitions that require accurate round velocities.
Prior laboratory methods for measuring exit velocity include: yaw screens, inductive rings, foil strain gages, bore pressure sensors, MEMs device in round and muzzle velocity radar. Prior field methods for measuring exit velocity include: MEMS devices in round, inductive rings and muzzle velocity radar.
The prior laboratory methods listed above are not suited for field conditions. Yaw screens are inductive wire loops on stands that are set up down range of the projectile near the muzzle. By design they are only useful in range testing situations. Foil strain gage systems are affected adversely by electromagnetic interference, require frequent calibration, zeroing and adjustment, and do not have the required bandwidth for high velocity projectiles. Bore pressure transducer-based methods require significant modifications to the barrel that are not conducive to field application since they require drilling through the barrel into the bore for insertion of the sensors.
This modification weakens the barrel and provides a potential path for water and contaminants to enter the bore. Muzzle velocity radar is expensive, bulky, emits significant electromagnetic radiation markedly increasing the risk of detection, and is typically only able to measure the round exiting velocity for the first round in a burst in automatic mode. MEMS devices in the round are expensive and take up valuable space.
The prior field methods are also unsatisfactory. A fielded inductive ring based system places three heavy inductive rings outboard of the muzzle blast area to measure the round exiting velocity. The addition of this significant extra mass degrades the performance of the gun stabilization system and adversely affects the gun system dispersion. Fielded muzzle velocity radars, similar to their laboratory grade cousins mentioned above, are costly, bulky, emit electromagnetic radiation thereby markedly increasing the risk of detection, and are typically only able to measure the round exiting velocity for the first round in an automatic burst mode.
The invention solves the problem of being able to determine the exiting velocity of the round in a reliable, accurate and cost-effective manner. It accomplishes this for any gun system by utilizing direct strain measurements made on the gun barrel using surface mounted or embedded fiber optic sensors. The measurements can be made for single shot or automatic rapid firing modes. The round exit velocity measurement can be used for air burst munitions system applications to enable precise bursting at desired range and improvement of ballistic solutions leading to improved projectile on target performance.
The invention provides a cost effective means to accurately measure the round exit velocity from a broad spectrum of gun barrels. The invention is rugged and can withstand shock, vibrations and high temperatures typically found on gun barrels. The invention is designed to measure high sampling rates of rapid-fire munitions so that each round can be interrogated and given the proper information with regards to time to burst. Temperature compensation as the gun barrel heats up has been incorporated into the invention to maintain accurate velocity measurements during the full firing scenario.